For the past five years this unit has focused on the extensive changes in LDL that occur as a result of oxidative modification. We have generated a panel of antibodies that recognize epitopes present on oxidized LDL (Ox-LDL) but not native LDL. We utilized these to demonstrate the presence of Ox-LDL in atherosclerotic lesions in rabbits and humans. In addition, we have shown that the modifications of LDL that occur during oxidation render Ox-LDL immunogenic and can lead to an autoantibody response which is directed specifically to the modification of LDL. We have shown that autoantibodies are present in the plasma of rabbits and humans that recognize epitopes of Ox-LDL, and we now propose to study the potential importance of such autoantibodies, to determine whether they are epiphenomena (i.e. are only markers for disease) or whether they have clinical consequences. We will determine the prevalence of autoantibody titers to epitopes of Ox-LDL in normal, cholesterol-fed and WHHL rabbits and relate the findings to age, sex and development of atherosclerotic lesions. We will experimentally induce a high titer of autoantibodies in WHHL rabbits and determine if this affects the rate of formation and/or the composition of atherosclerotic lesions. We will characterize the antibodies found in rabbit lesions and determine if they are present as part of immune complexes and whether or not circulating immune complexes are also present. Finally, we will determine if autoantibodies exist in other conditions in which lipid peroxidation is known to be enhanced, such as in rats fed a diet high in iron. We will determine if early stages of Ox-LDL can be detected in animals undergoing perturbations that should increase lipid peroxidation, such as cholesterol feeding, a high polyunsaturated diet, or vitamin E deficiency, and conversely whether conditions known to inhibit oxidative modification, such as treatment with probucol or vitamin E, will decrease the presence of such markers. We will utilize our panel of antibodies to study aortic tissue from a variety of animal models to determine if Ox-LDL is a consistent component of lesions and we will study tissue obtained from the PDAY Study to determine the prevalence of Ox-LDL in human aortic samples. Finally, we will study WHHL rabbit xanthomas to look for the presence of Ox-LDL and to determine if the lipid-filled macrophages found in xanthomas are generated by the same process that we believe -occurs in the artery. These studies should help define the metabolic and immunologic consequences that occur when LDL is oxidatively, modified.